On 1/18/22 17:27, Emanuele Giuseppe Esposito wrote:
Depending on the options given to reopen_state,
bdrv_reopen_parse_file_or_backing could pick another bs
that could be from another graph, and thus not protected
by subtree_drained_begin called by the callers of this
function.
We can't simply drain-undrain here, because of transactions.
To simplify the logic, transactions always assume that they
are run under drain, so the various subtree_drain introduced
so far always take care of covering tran_commit().
And since we cannot directly do it, as the transaction is
created/committed higher above, we can just add a new
transaction to the list that just executes subtree_drained_end
to match the drained_begin done in this function.
A rewrite of the last two paragraphs:
---
Of the two callers of bdrv_set_file_or_backing_noperm,
bdrv_reopen_parse_file_or_backing is unique in that it does not complete
the reopen, it only prepares a transaction. The actual commit (or
abort) is done higher in the call chain.
Therefore, the call to bdrv_subtree_drained_end_unlocked must be delayed
until after the transaction's fate has been determined and its actions
have been performed. Do this by recording a TransactionActionDrv to end
the drained section for new_child_bs.
---
Likewise, the subject can be "block: keep children drained across a
reopen transaction"; explain the change and not the technicalities of
how you did it.
Paolo
Signed-off-by: Emanuele Giuseppe Esposito <eespo...@redhat.com>
---
block.c | 25 ++++++++++++++++++++-----
1 file changed, 20 insertions(+), 5 deletions(-)
diff --git a/block.c b/block.c
index fb5bc3077a..fcc44a49a0 100644
--- a/block.c
+++ b/block.c
@@ -4522,6 +4522,10 @@ int bdrv_reopen_set_read_only(BlockDriverState *bs, bool
read_only,
return bdrv_reopen(bs, opts, true, errp);
}
+TransactionActionDrv bdrv_drv_subtree_end = {
+ .clean = (void (*)(void *)) bdrv_subtree_drained_end_unlocked,
+};
+
/*
* Take a BDRVReopenState and check if the value of 'backing' in the
* reopen_state->options QDict is valid or not.
@@ -4550,6 +4554,7 @@ static int
bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
const char *child_name = is_backing ? "backing" : "file";
QObject *value;
const char *str;
+ int ret = 0;
assert(qemu_in_main_thread());
@@ -4573,6 +4578,8 @@ static int bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
"cycle", str, child_name, bs->node_name);
return -EINVAL;
}
+ /* This will be paired with a drained_end in tran_commit */
+ bdrv_subtree_drained_begin_unlocked(new_child_bs);
break;
default:
/*
@@ -4583,18 +4590,19 @@ static int
bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
}
if (old_child_bs == new_child_bs) {
- return 0;
+ goto end;
}
if (old_child_bs) {
if (bdrv_skip_implicit_filters(old_child_bs) == new_child_bs) {
- return 0;
+ goto end;
}
if (old_child_bs->implicit) {
error_setg(errp, "Cannot replace implicit %s child of %s",
child_name, bs->node_name);
- return -EPERM;
+ ret = -EPERM;
+ goto end;
}
}
@@ -4605,7 +4613,8 @@ static int bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
*/
error_setg(errp, "'%s' is a %s filter node that does not support a "
"%s child", bs->node_name, bs->drv->format_name,
child_name);
- return -EINVAL;
+ ret = -EINVAL;
+ goto end;
}
if (is_backing) {
@@ -4614,8 +4623,14 @@ static int
bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
reopen_state->old_file_bs = old_child_bs;
}
- return bdrv_set_file_or_backing_noperm(bs, new_child_bs, is_backing,
+ ret = bdrv_set_file_or_backing_noperm(bs, new_child_bs, is_backing,
tran, errp);
+
+end:
+ if (new_child_bs) {
+ tran_add(tran, &bdrv_drv_subtree_end, new_child_bs);
+ }
+ return ret;
}
/*